Interleukin-6 ablates the accessory cell-mediated suppressive effects of lactoferrin on human hematopoietic progenitor cell proliferation in vitro

Lactoferrin: a tamoxifen-responsive protein in normal and malignant human endometrial cells in culture

We investigated the possible role of the estrogen-regulated protein lactoferrin (Lf) in the response of isolated normal human endometrial epithelial cells (NHEC) and established human endometrial carcinoma (EC) cell lines to tamoxifen (TAM). Using confocal laser scanning microscopy and a monospecific antibody, Lf was localized to the cytoplasm of normal and EC cells. Antibody neutralization of secreted Lf inhibited, whereas exogenous Lf (0--100 microg/ml) enhanced, cell proliferation in both classes of cells. Treatment of NHEC with TAM inhibited cell growth via a protein kinase-C-mediated pathway, concomitant with a reduction in the staining intensity for Lf. Importantly, in EC cells, TAM greatly enhanced the staining intensity for Lf, but did not affect cell growth. We propose that stable expression of Lf protein by EC cells may impart a survival advantage to these cells, which may, in part, account for the resistance of these cells to tamoxifen.

Estrogen regulation of lactoferrin expression in human endometrium

PROBLEM

Lactoferrin is an iron-binding glycoprotein that has been shown to be overexpressed in human endometrial carcinomas. The purpose of our present study is to investigate the possible role of estradiol in the expression of lactoferrin.

METHOD OF STUDY

We investigated 1) serum levels of lactoferrin in five women during normal ovulatory cycles, 2) serum levels of lactoferrin during ten human menopausal gonadotropin induced cycles when estradiol levels are high, and 3) lactoferrin expression in five proliferative and five secretory phase endometrium by immunohistochemical studies. The serum concentrations of lactoferrin were measured by a peroxidase-based enzyme-linked immunosorbent assay.

RESULTS

In normal ovulatory cycles, the mean serum lactoferrin concentration during the proliferative phase (0.4013 +/- 0.0242 micrograms/mL) was significantly higher (P < 0.02) than in the secretory phase (0.3468 +/- 0.0209 micrograms/mL). In induced cycles, there was gradual increase in lactoferrin levels with increasing estradiol concentrations. Peak lactoferrin levels in induced cycles (0.7495 +/- 0.1148 micrograms/mL) were significantly higher (P < 0.003) than the midcycle levels (0.423 +/- 0.0424 micrograms/mL) in normal cycles. Immunohistochemical analysis of the endometrium revealed greater expression of lactoferrin in proliferative endometrium (50.7 +/- 13%, range 28-72%) than in secretory endometrium (19.2 +/- 4%, range 7-31%).

CONCLUSION

These results indicate that estradiol may play a role in the regulation of lactoferrin expression in human endometrium.

Feedback inhibitors in normal and tumor tissues

Negative feedback represents the principal mechanism for regulating growth in biological systems. Over the past 20 years, our understanding of the role played by inhibitory factors governing this process has advanced considerably. This is particularly well illustrated in the field of experimental hematology with the recognition of hemopoietic progenitor cell proliferation inhibitors, an expanding group of unrelated peptides that act to limit proliferation in hemopoietic precursor cells. The characterization and subsequent production of these molecules by chemical synthesis or recombinant DNA technology has enabled investigators to explore their role in normal hemopoiesis and define a potential role in clinical medicine. A number of inhibitory factors, including macrophage inflammatory protein-1 alpha (MIP-1 alpha) and the tetrapeptide AcSDKP appear to share a relative specificity to hemopoietic progenitor cell subsets. Others, such as interferon and tumor necrosis factor, have a more complex action and their hemopoietic effects are likely to be indirect and nonspecific. In addition to the role of inhibitors in normal steady state, it has become increasingly evident that loss of sensitivity to the normal feedback inhibitory signals may be of central importance in carcinogenesis and tumor promotion. This presumably represents a developmental strategy that allows the neoplastic cell to maintain a growth advantage over its normal cell counterpart. The underlying mechanisms that terminate in inhibitor-resistance are yet to be elucidated, but in some instances they may be associated with aberrant tumor suppressor gene function.

Physical characteristics and polymerization during iron saturation of lactoferrin, a myelopoietic regulatory molecule with suppressor activity

Lactoferrin (LF) has been implicated in normal regulation of myeloid blood cell production in vitro and in vivo and abnormalities in LF-cell interactions have been associated with progression of leukemia and other hematopoietic disorders. LF may be clinically useful and for this reason we studied selected biochemical characteristics of LF. Purified human milk LF was saturated with iron from solution and analyzed by gel electrophoresis, ion-exchange and gel filtration chromatography. The metalloprotein was found to contain several molecular weight species on polyacrylamide gels. High resolution ion-exchange chromatography demonstrated the binding of LF to both anionic and cationic media under identical conditions indicating a bipolar charge distribution. Gel filtration studies revealed a tetramerized form of LF, the formation and stability of which was dependent on the ionic strength of the solution.